The invention is related to brake pressure control systems for automotive vehicles having an anti-locking control system (ABS) and/or with a traction slip control system (TSS), which is operated with fluid, in particular with hydraulic fluid pressure Such systems typically include a master cylinder, one or more wheel cylinders for wheel brakes, and a pressure modulator comprising a plurality of valves for the modulation of the hydraulic pressure in the wheel cylinders of the wheel brakes during a brake pressure control mode. At least one motor-driven pump is usually employed for generat[ion]ing fluid hydraulic pressure, and an electronic controller for controlling the valves and the pump.
An example of such a brake system is described in German patent application published without examination, No. 3,731,603.
As noted, brake systems of this kind equipped with an anti-locking control system and/or with a traction slip control system are furnished with one or two auxiliary pumps which deliver pressurized fluid into the pressure modulator during the anti-locking control mode. The pressure modulator comprises a plurality of hydraulic valves. In particular, sets of inlet and outlet valves are provided in the pressure modulator which are associated with respective wheel cylinders.
The driver stage of the electronic controller operates the inlet and outlet valves in accordance with the control algorithm incorporated in the controller.
A pressure reduction phase is generated in the wheel cylinder when the outlet valve is open and the inlet valve is closed. When the inlet valve is closed and the outlet valve is closed a pressure stabilization phase comes about. When the inlet valve is open and the outlet valve is closed a pressure rebuilding-up phase ensues.
Furthermore, hydraulic connections have been described in which the inlet valve has a restrictive effect. See German patent application P 3,919,842.1.
In that patent application, a hydraulic brake unit for a vehicle is described which is equipped with an anti-locking control system, with a master cylinder, a fluid pressure accumulator, at least one wheel brake which is connected to the master brake cylinder through a brake line and is in connection with the fluid pressure accumulator through a return line. An electromagnetically actuated outlet valve is inserted in the return line which shuts off the return line in its normal position and opens the retain line in its switching position. A restriction valve is installed in the brake line and is furnished with two switching positions, an unrestricted connection existing between the wheel brake and the master brake cylinder in the first switching position and a restricted connection existing between the wheel brake and the master brake cylinder in the second switching position. A pump aspirates fluid from the accumulator and delivers it through a pressure line into the master cylinder. A sensor monitors the angular velocity of the wheel to be braked and an electronic evaluation unit evaluates the sensor signal and generates switching signals for the pump drive and for the outlet valve.
It is proposed in the forementioned German patent application that the restriction valve is connected by means of a control line to the outlet of the pump so that the pressure at the outlet of the pump shifts the restriction valve from the first into the second switching position.
In the embodiments as per FIGS. 4 to 7 of the German patent application published without examination, No. 3,731,603 an electric driving motor for a pump for hydraulic brake systems are described whose rotor is axially movable.
In practice it has proved to be desirable to be able to switch more rapidly than has been possible as yet the inlet valves of the pressure modulators of the state of the art, for example, the NO valves, open when deenergized of the subject matter of the above-mentioned patent application published without examination, or the inlet valves with restricting function of the subject matter of the above-mentioned earlier patent application.
The present invention has the following objects:
The inlet valves for the wheel cylinders of brake units such as those described above are to be switched more quickly than is possible according to the state of the art. The definition "inlet valve" has to be understood to have a general meaning. Indeed, the matter may be about inlet valves in accordance with the above-mentioned German patent application published without examination, in accordance with the above-mentioned earlier German patent application No. P 3,919,842.1 in which the inlet valves perform a restricting function, or about other types of inlet valves which serve to control the brake pressure in the wheel cylinder. It is, in particular, the object of the invention to achieve a very rapid pressure reduction in the wheel cylinder during the control mode. Furthermore, the pedal feeling is to be improved.